4-Allyloxystyrene and compositions derived from this monomer are known and are disclosed as particularly useful for the production of photocured polymers and thermally resistant adhesives in McArdle et al, U.S. Pat. No. 5,084,490, (1992) and McArdle et al, U.S. Pat. No. 5,141,970, (1992). 4-Allyloxystyrene and related materials have also previously been found to be useful for the production of cationically polymerizable telechelic polymers as reported in Woods, et al, U.S. Pat. No. 4,543,397, (1985), and Woods et al, U.S. Pat. No. 4,732,956, (1988). In all of these cases, the 4-allyloxystyrene monomer was prepared in two separate stages involving firstly the conversion of 4-hydroxybenzaldehyde to 4-allyloxybenzaldehyde, by alkylation of the phenol with allyl bromide. In the second stage, the 4-allyloxybenzaldehyde was converted to 4-allyloxystyrene in a Wittig Reaction utilizing methyltriphenylphosphonium bromide. In all cases it was found to be necessary to isolate and purify the intermediate 4-allyloxybenzaldehyde by vacuum distillation prior to proceeding to the Wittig reaction stage. The synthesis of 4-allyloxystyrene by the Wittig route is outlined in Scheme 1. ##STR3##
4-Allyloxystyrene is also a useful diluent in other cationically polymerizable systems, particularly those based on vinyl ethers such as disclosed in Klemarczyk et al, U.S. Pat. No. 5,070,117, (1991), and references cited therein.
Despite the many advantages of compositions derived from 4-allyloxystyrene, it has not been possible to develop commercial products based on these materials due to the high costs associated with the above synthetic methodology. In the first stage, the starting reagents, 4-hydroxybenzaldehyde and methyltriphenylphosphonium bromide, are needed in stoichiometric quantities and are costly materials. In the second stage, the Wittig reaction is particularly difficult and time consuming in relation to the removal of the unwanted byproduct, triphenylphosphine oxide. This material is the major product of the Wittig reaction and accounts for 63% of the crude product weight. The phosphine oxide is very soluble in 4-allyloxystyrene and separation requires careful precipitation of the oxide with large amounts of petroleum ether to reduce the concentration to a sufficient level to permit vacuum fractionation to be successful. Large-scale production of allyloxystyrene by this method is therefore costly by comparison to the production of other reactive monomers such as acrylates, epoxies or vinyl ethers.
The synthesis of the unalkylated monomer, 4-hydroxystyrene from 4-acetosystyrene is reported in Sheehan et al, U.S. Pat. No. 5,087,772, (1992). This reference states that aqueous saponification of 4-acetoxystyrene with potassium hydroxide results in the polymerization of the monomer and that a catalytic amount of base, such as potassium hydroxide at a concentration of 0.5-3.0 mole %, is critical in order to prevent the polymerization of the acetoxystyrene. The reaction of this reference is performed in the presence of excess alcohol and the acetic acid is removed in the form of the corresponding acetate.
Crivello, et al, J.M.S.--Pure Appl. Chem., A29(9), pp 753-774 (1992), describes syntheses of isopropenylphenyl ether compounds by the condensation of 4-acetoxystyrene or 4-isopropenylphenyl acetate with .alpha., .omega.-dihaloalkanes, or 2-chloroethyl vinyl ether in the presence of base.